This invention relates generally to switching apparatus of the type used in electrical transformers, for example, and more particularly, but not by way of limitation, to a compound tandem switching apparatus for interconnecting selectable ones of a plurality of tapped sections of a plurality of windings of a transformer.
It is, of course, well known that electrical transformers include primary and secondary windings which can have tapped sections which are selectably interconnectable so that different outputs can be obtained from the transformer. An example of such a transformer is shown in U.S. Pat. No. 4,160,224 in the name of Owen. The selectable interconnections are often made by a manual switching apparatus, one example of which is also illustrated in U.S. Pat. No. 4,160,224. Exemplary switching apparatus is claimed in U.S. Pat. No. 4,256,932, also in the name of Owen.
Such manual switching apparatus have been of the rotary type wherein a circular array of terminals are switchably connectable to a common terminal by a rotatable wiper arm which makes and breaks contact with the terminals along the same line or path on which the terminals are disposed. The wiper arm of such a switch is turned either by a rotary motion as exemplified in U.S. Pat. No. 4,160,224 or by a linear motion as believed to be exemplified in U.S. Pat. No. 726,391 in the name of Armstrong et al.
Although such prior art switching apparatus are functional, they do have certain disadvantages. For examle, such a rotary switching apparatus often requires substantial space which necessitates the use of a larger container in which the transformer is to be retained. This requirement for substantial space is brought about by, for example, the curvilinear disposition of the terminals, the allowance of space for making the lead connections to the terminals, and the size of the rotary mechanism. Therefore, there is a need for a more streamlined switching apparatus which does not require as much space, at least in one dimension, as such prior rotary types.
Such larger prior switching apparatus also require relatively long leads from the tapped sections to the switch terminals. Because a longer lead of a given diameter and material has a greater resistance than a shorter lead of the same diameter and material, there is a greater loss when the longer lead is used. Therefore, there is also the need for a switching apparatus which permits the use of a reduced lead length, thereby reducing electrical losses.
Such prior art switching apparatus also can be constructed so that the leads from the transformer windings to the connection terminals must be criss-crossed or so that leads between terminals of the switching apparatus must be criss-crossed. Such criss-crossing makes the connections more difficult to make; therefore, there is the need for a new switchig apparatus which enables a simplified lead connection array.
Furthermore, in these prior switching apparatus wherein the path of the portion of the wiper arm which makes contact with the terminals is along the line on which the terminals are disposed, there is the tendency during use thereof for the wiper arm to remove a portion of the conductive material of which the terminals are formed and to drag the removed material along the line toward the next terminal as the wiper arm is moved from one terminal to the next. It is apparent that after extended use of such an apparatus, the removed material can create an electrically conductive path between the adjacent terminals, thereby creating a short-circuit and a potential safety hazard. Thus, there is the need for a switching apparatus which does not tend to construct such a conductive bridge between adjacent terminals.